1. Field of the Invention
The present invention generally relates to semiconductor substrate processing systems. More specifically, the present invention relates to a method and apparatus for monitoring an etch process.
2. Description of the Related Art
To increase operational speed, devices (e.g., transistors, capacitors, and the like) in integrated microelectronic circuits have become ever smaller. One method of fabricating such devices comprises forming a patterned mask (e.g., photoresist mask) on a material layer formed on a substrate and then etching the material layer using the patterned mask as an etch mask. The etch mask generally is a replica of the structure being formed (i.e., etched) in the underlying material layer (or layers). As such the etch mask has the same topographic dimensions as the structures to be formed in the underlying layer(s).
Typically, the smallest widths for elements of an etch mask, such as lines, columns, openings, spaces between lines, and the like are measured. Such smallest widths are known as “critical dimensions”, or CDs. In advanced ultra large scale integrated (ULSI) circuits, the critical dimensions are generally sub-micron dimensions of about 20 to 200 nm. Additionally, thickness measurements for material layers to be etched are ascertained. Parameters for an etch process recipe are generally selected using statistically generated results of the critical dimension measurements of the patterned masks formed on wafers as well as the thickness measurements of material layers to be etched.
Accurate etch process monitoring is critical when etching a material layer using a patterned mask. In particular, manufacturing variables for the etch process may decrease dimensional accuracy of devices formed therewith, as well as cause a broad statistical distribution (i.e., a large σ, where is σ a standard deviation) for the dimensions of devices formed on substrates within a group (i.e., batch) of substrates.
Therefore, there is a need in the art for improved etch process monitoring in the fabrication of integrated circuits.